(1) Field of the Invention
The invention relates to the fabrication of integrated circuit devices, and more particularly, to a method and apparatus for assuring constant flow of fluids that are used in the preparation of chemical solutions.
(2) Description of the Prior Art
In preparation for and during the creation of semiconductor devices, it is frequently required to provide chemical solutions in fluid form that are used during the manufacturing of semiconductor devices. These fluids may be pure, undiluted chemicals or, as is more often the case, they may be fluids that contain a mixture of several chemicals that combined and are aimed at performing a particular processing step in the sequence of creating semiconductor devices. As a basic example can be cited the use of DI water, which is frequently used for purposes of rinsing surfaces that have been processed in order to remove remnants of chemicals that have been used during the processing of a semiconductor substrate. In preparing a chemical mix, such as 50:1 or 10:1 HF, which is a solution that is frequently applied to for instance remove oxidized Plasma Polymerized Methylsilane (PPMSO) after a buffer oxide etch has been applied to the PPMS, it is critical that the solution of HF contains the correct proportion and the correct chemical dilution that is required for the application of the HF solution. A HF dip is typically a one-time process performed at atmospheric pressure using a conventional wet bench process with a gas source of H2O:HF=100:1 for a duration of about 90 seconds. This latter example is indicated at this time to indicate that precise control of the proportion and the dilution consistency are important to the success of a chemical process and are part of a number of control parameters that apply to this process.
In providing or preparing chemical solutions in fluid form for the processing of semiconductor devices, these solutions and their derivatives are frequently passed through a fluid distribution system. A fluid distribution system typically consists of a tubular arrangement where the total distribution system potentially contains a large number of branches or points of division such that the fluids can be provided at the desired points of use of the fluids. It is clear that a fluid distribution system can therefore be very complex, which makes the requirement of even and controlled flow of the fluid through all components of the fluid distribution system that more demanding. Fluid distribution systems have, for many applications, a return loop so that the fluid distribution system is a closed loop system. Fluids that have been used can, after the application of the fluids has been completed, be treated in order to restore the fluids to an original condition for further reuse. This process has obvious advantages of cost control. Fluids that pass through a fluid distribution system may further be subjected to additional actions such as temperature control and other environmental control of the fluids in order to prepare the fluids for specific processing steps. This activity as yet adds further complexity to the requirement that the correct proportion and the correct consistency of the fluids must be controlled at all points in the fluid distribution system.
Prior Art devices and methods that are to assure fluid consistency are typically applied at the point-of-use (POU). This method of control is, in many respects, an xe2x80x9cafter the factxe2x80x9d method of control in that the POU validation method only observes fluid consistency at the point where the fluid is applied rather than at frequent validation points that are strategically placed within the loop or the system that provides the fluids. The reason that makes the POU method attractive is the high cost of the currently used flow control valves. The flow control valves, in applying the POU method of control, are subjected to a relatively heavy duty method of use and are therefore prone to require frequent replacement and/or frequent maintenance support.
An improved method and apparatus of controlling fluid flow in a fluid distribution system is therefore of benefit for a semiconductor manufacturing environment. The invention provides such an improved method and apparatus.
U.S. Pat. No. 4,855,023 (Clark) shows an apparatus for an on-site chemical reprocessing of liquid having tanks.
U.S. Pat. No. 4,917,123 (McConnell et al.) shows a wafer cleaning station having tanks and a Mace valve.
U.S. Pat. No. 4,483,357 (Rao et al.) shows a 2-stage in-line acid mixing setup with tanks.
A principle objective of the invention is to provide a method and apparatus that assures constant pressure fluid distribution in a semiconductor processing environment.
Another objective of the invention is to provide a method and apparatus that assures consistent fluid distribution in a semiconductor-processing environment.
Yet another objective of the invention is to provide a method and apparatus to negate effects of random pressure and/or flow variations in a fluid distribution system, enabling consistent fluid distribution in a semiconductor processing environment that is not affected by outside influences.
A still further objective of the invention is to provide a method and apparatus that negates any effects of a sudden surge in demand for fluid at a particular point in the fluid distribution system thus assuring consistent fluid distribution at all points that are supplied by the fluid distribution system.
In accordance with the objectives of the invention a new method and apparatus is provided that assures constant fluid flow of the fluid that is entered into a semiconductor device processing tank or container. A flow meter is set to a particular flow rate, the fluid that comes from the POU is routed through the flow meter. The fluid that leaves the flow meter runs into a processing tank or container. It is the objective of the method and apparatus of the invention to keep the flow of the fluid through this container at a constant flow rate. The fluid is allowed to fill the container up to an overflow point of the container, the fluid is not allowed to go over this level. An overflow basin is therefore provided for the fluid into which the overflowing fluid is allowed to run. Once the fluid reaches the overflow level of the container, the fluid runs into an overflow catch basin (which is part of the fluid container) from where the fluid is drained into a fluid reclaim vessel via a basin conduit. This occurrence of the overflow (the fluid running from the overflow basin to the fluid reclaim vessel) is detected by a sensor, the sensor activates an overflow relieve valve that is mounted in the bottom of the container. The overflow relieve valve is opened and drains fluid from the container thus counteracting the overflow of the fluid into the overflow basin. The interaction between the overflow detector and the overflow relieve valve assures (dependent on the interrelation of the fluid flow through the entry valve and the overflow relieve valve) a constant rate of supply of the fluid to the processing tank or container.